Add JoinGroup v1 structs (#965)
Add JoinGroup v1 structs (#965)

The JoinGroupRequest struct added a rebalance_timeout as part of KIP-62 / KAFKA-3888
Yelp/kafka-python,ohmu/kafka-python,wikimedia/operations-debs-python-kafka,dpkp/kafka-python,Aloomaio/kafka-python,dpkp/kafka-python,mumrah/kafka-python,DataDog/kafka-python,Yelp/kafka-python,scrapinghub/kafka-python,ohmu/kafka-python,mumrah/kafka-python,Aloomaio/kafka-python,wikimedia/operations-debs-python-kafka,scrapinghub/kafka-python